Invasive micropapillary carcinoma (IMPC) is a rare type of breast cancer with high frequency of regional lymph node metastasis. However, the prognosis of IMPC has remained controversial for decades. We aimed to compare the differences of prognosis between IMPC and Invasive ductal carcinoma(IDC) of the breast by utilizing Surveillance, Epidemiology, and End Results (SEER) database.

1. Clinics of Oncology
Research Article ISSN: 2640-1037 Volume 6
Prognosis of Invasive Micropapillary Carcinoma of the Breast Analyzed by Using the
SEER Database
Lang Qin1
, Chuanbo Xie2
, Kaitao Yuan3
, Tiantian Zhen4
, Ying Lin1*
and Nan Shao1*
1
Breast Disease Center, The First Affiliated Hospital, Sun Yat-sen University, No.58 Zhongshan 2nd Road, Guangzhou 510080, China
2
Cancer Prevention Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine,
Sun Yat-sen University Cancer Center, Guangzhou 510080, China
3
Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, No.58 Zhongshan 2nd road, Guangzhou
510080, China
4
Department of Pathology, the First Affiliated Hospital of Sun Yat-Sen University, Guangzhou 510080, Guangdong Province, China
*
Corresponding author:
Nan Shao and Ying Lin,
Breast Disease Center, The First Affiliated
Hospital, Sun Yat-sen University, No.58
Zhongshan 2nd Road, Guangzhou 510080, China,
Tel: 8620-87755766 ext. 8198,
E-mail: shaon@mail.sysu.edu.cn and
linying3@mail.sysu.edu.cn
Received: 10 Apr 2022
Accepted: 09 May 2022
Published: 13 May 2022
J Short Name: COO
Copyright:
©2022 Nan Shao and Ying Lin. This is an open access ar-
ticle distributed under the terms of the Creative Commons
Attribution License, which permits unrestricted use, distri-
bution, and build upon your work non-commercially.
Citation:
Nan Shao and Ying Lin, Prognosis of Invasive Micropapil-
lary Carcinoma of the Breast Analyzed by Using the SEER
Database. Clin Onco. 2022; 6(6): 1-8
Keywords:
IMPC; IDC; Breast cancer; Survival; Prognosis
clinicsofoncology.com 1
1. Abstract
1.1. Background: Invasive micropapillary carcinoma (IMPC) is a
rare type of breast cancer with high frequency of regional lymph
node metastasis. However, the prognosis of IMPC has remained
controversial for decades. We aimed to compare the differences of
prognosis between IMPC and Invasive ductal carcinoma(IDC) of
the breast by utilizing Surveillance, Epidemiology, and End Re-
sults (SEER) database.
1.2. Material and Methods: Patients diagnosed with IMPC and
IDC between 1 January 2010 and 31 December 2016 from the
SEER database were retrieved. Propensity score matching was
used to match the two groups at a 1:1 ratio. Breast cancer-specific
survival (BCSS) and overall survival (OS) rates were compared
between IMPC and IDC using Kaplan-Meier estimates, Log-rank
tests, univariate and multivariate Cox proportional hazard models.
Stratification analyses on breast subtype were also performed.
1.3. Results: A total of 921 patients with IMPC and 173, 621 pa-
tients with IDC were included in the present retrospective study.
IMPC had more regional node metastasis than IDC (48.97% vs.
31.41%, p<0.05). IMPC had a better prognosis than IDC as shown
by both the BCSS (p<0.01) and OS (p=0.03) but shared the same
prognosis after PSM. IMPC had a better OS (p=0.04) and less dis-
tant metastasis (p=0.04) in the HR+/HER2- breast subtype than
IDC.
1.4. Conclusion: IMPC had more axillary lymph nodes metastasis
than IDC. Despite aggressive regional invasion, IMPC had a sim-
ilar outcome compared with IDC in the BCSS and OS after PSM.
Furthermore, IMPC had a better overall survival rate and less dis-
tant metastasis than IDC in the HR+/HER2- group.
2. Introduction
Invasive micropapillary carcinoma (IMPC) of the breast was first
noted in 1980, defined as a pathological subtype by Siriaunkgul
and Tavasol in 1993 [1], and listed in the World Health Organi-
zation (WHO) tumor histologic classification in 2003 [2]. IMPC
accounts for approximately 6% of all invasive breast cancers [3].
The pathology of IMPC is characterized by tufts of cells arranged
in pseudopapillary structures devoid of fibrovascular cores and
surrounded by empty, clear spaces lined by delicate strands of fi-
brocollagenous stroma [4], with EMA and MUC-1 expressed on
the basal surface of the cells [5]. In addition, IMPC is known for its
high propensity for lymphatic vessel invasion and regional lymph
node metastasis [1,3,6], which might cause a worse prognosis than

2. clinicsofoncology.com 2
Volume 6 Issue 6 -2022 Research Article
invasive ductal carcinoma (IDC). Previous studies demonstrated
that there was no difference in the prognosis of IMPC and IDC [7-
11]. In contrast, another study found that IMPC had a better prog-
nosis than IDC despite its highly aggressive clinical presentation
[12]. In a recent meta-analysis, IMPC exhibited a similar, even
favorable, overall survival rate but a shorter relapse-free survival
rate than IDC [13]. There was no consensus on IMPC prognosis
and treatment worldwide to date. In this retrospective study, we
analyzed the survival rate of IMPC and IDC by using the Surveil-
lance, Epidemiology, and End Results (SEER) database.
3. Materials and Methods
3.1. Data source and Patient Selection
Data were retrieved from the National Cancer Institute’s Surveil-
lance, Epidemiology, and End Results (SEER) 18 registry data-
base released in April 2019 by the v8.3.8 SEER*Stat program.
The ICD-O-3 (International Classification of Diseases for Oncol-
ogy Version 3) codes of IMPC and IDC were 8507 and 8500/3,
respectively. Since HER2 (human epidermal growth receptor 2)
status records were available after 2010 in the SEER database, we
chose IMPC and IDC patients diagnosed between 1 January 2010
and 31 December 2016. Search criteria were restricted to patients
who were female, had confirmed histology of invasive carcino-
ma and whose tumor was a primary occurrence. Exclusion crite-
ria including bilateral breast cancer, autopsy or death certification
reports, unknown American Joint Committee on Cancer (AJCC)
TNM stage (7th edition), unknown estrogen receptor (ER)/proges-
terone receptor (PR)/HER2 status, unknown pathological grade or
surgery type and stage IV disease.
3.2. Propensity Score Matching
To avoid bias and balance the basic characteristics for the analysis,
we performed 1:1 propensity score matching (PSM). PSM vari-
ables were selected as follows: age, histologic grade, T stage, N
stage, ER, PR, and HER2 status.
3.3. Statistical Analysis
The primary outcomes were the breast cancer-specific survival
(BCSS) and overall survival (OS) rates. The BCSS rate was de-
fined as the time from disease occurrence to the date of death due
to breast cancer and the OS rate was defined as the time from dis-
ease occurrence to the date of death due to any cause.
Univariate and multivariate Cox proportional hazards models were
generated to assess the unadjusted and adjusted odds ratios (ORs)
with 95% CIs (confidence intervals) of the various characteristics
of IMPC patients. To confirm the difference in regional node me-
tastasis, Mann-Whitney tests were conducted for positive lymph
nodes depending on T stage. All analyses were performed via
SPSS statistical software, version 25.0 (Armonk, NY, IBM Crop).
A two-sided p < 0.05 was considered to indicate statistical signif-
icance.
4. Results
4.1. Characteristics of IMPC and IDC
Based on the inclusion and exclusion criteria, 921 patients with
IMPC and 173,621 patients with IDC were included (Figure 1).
Compared to the IDC, the IMPC had more advanced stage and
more nodal metastasis (stage III: 22.37% vs. 11.26%, T3/T4 stage:
11.40% vs. 7.37%, nodal metastasis: 48.97% vs. 31.41%). As
for nodal metastasis, IMPC metastasized more than IDC at any
T stage (p<0.05) (Figure 2). In terms of subtype, the IMPC had
a higher proportion of ER-positive (91.21% vs. 80.77%, p<0.01)
and PR-positive (81.76% vs. 70.97%, p<0.01), and the triple-neg-
ative subtype accounted for only 4.0% of IMPC patients. In addi-
tion, a higher percentage of IMPC patients received chemotherapy
(52.55% vs. 44.87%, p<0.01) and radiation therapy (61.13% vs.
55.12%, p<0.01). The types of surgery distributed similarly be-
tween the two histological types (p=0.13).Acomplete 1:1 matched
case-control study by the propensity score match (PSM) method
was performed. A total of 917 IMPC patients were completely
matched to another 917 IDC patients (Table 1). In PSM cohort,
compared to IDC, IMPC group were treated with similar type of
surgery (p=0.68), chemotherapy (p=0.58) and radiation (p=0.10).
Figure 1: Flow chart of selecting records of patients with SEER database.

3. clinicsofoncology.com 3
Volume 6 Issue 6 -2022 Research Article
Figure 2: Comparison of positive nodes in different T stages.
Table 1: Characteristics of IMPC and IDC in the whole/PSM cohort.
Whole cohort PSM cohort
Total IDC IMPC p Total IDC IMPC p
Characteristics n=174,317 n=173,396 n=921 n=1,834 n=917 n=917
Age 0.12 >0.99
>50 47,283 (27.12%) 47,054 (27.14%) 229 (24.86%) 452 (24.65%) 226 (24.65%) 226 (24.65%)
≤50 127,034 (72.88%) 126,342 (72.86%) 692 (75.14%) 1,382 (75.35%) 691 (75.35%) 691 (75.35%)
Tumor Stage <0.01 >0.99
T1 107,631 (61.74%) 107,117 (61.78%) 514 (55.81%) 1,028 (56.05%) 514 (56.05%) 514 (56.05%)
T2 53,801 (30.86%) 53,499 (30.85%) 302 (32.79%) 604 (32.93%) 302 (32.93%) 302 (32.93%)
T3 8,528 (4.89%) 8,451 (4.87%) 77 (8.36%) 148 (8.07%) 74 (8.07%) 74 (8.07%)
T4 4,357 (2.50%) 4,329 (2.50%) 28 (3.04%) 54 (2.94%) 27 (2.94%) 27 (2.94%)
Nodal Stage <0.01 >0.99
N0 119,396 (68.49%) 118,926 (68.59%) 470 (51.03%) 940 (51.25%) 470 (51.25%) 470 (51.25%)
N1 41,621 (23.88%) 41,335 (23.84%) 286 (31.05%) 568 (30.97%) 284 (30.97%) 284 (30.97%)
N2 8,887 (5.10%) 8,785 (5.07%) 102 (11.07%) 202 (11.01%) 101 (11.01%) 101 (11.01%)
N3 4,413 (2.53%) 4,350 (2.51%) 63 (6.84%) 124 (6.76%) 62 (6.76%) 62 (6.76%)
AJCC Stage <0.01 0.99
I 92,507 (53.07%) 92,117 (53.13%) 390 (42.35%) 783 (42.69%) 393 (42.86%) 390 (42.53%)
II 62,077 (35.61%) 61,752 (35.61%) 325 (35.29%) 647 (35.28%) 322 (35.11%) 325 (35.44%)
III 19,733 (11.32%) 19,527 (11.26%) 206 (22.37%) 404 (22.03%) 202 (22.03%) 202 (22.03%)
Histologic
Grade
<0.01 >0.99
I 36,402 (20.88%) 36,342 (20.96%) 60 (6.51%) 116 (6.32%) 58 (6.32%) 58 (6.32%)
II 72,630 (41.67%) 72,088 (41.57%) 542 (58.85%) 1,082 (59.00%) 541 (59.00%) 541 (59.00%)
III and IV 65,285 (37.45%) 64,966 (37.47%) 319 (34.64%) 636 (34.68%) 318 (34.68%) 318 (34.68%)
ER Status <0.01 >0.99
Negative 33,417 (19.17%) 33,336 (19.23%) 81 (8.79%) 160 (8.72%) 80 (8.72%) 80 (8.72%)
Positive 140,900 (80.83%) 140,060 (80.77%) 840 (91.21%) 1,674 (91.28%) 837 (91.28%) 837 (91.28%)
PR Status <0.01 >0.99
Negative 50,498 (28.97%) 50,330 (29.03%) 168 (18.24%) 330 (17.99%) 165 (17.99%) 165 (17.99%)
Positive 123,819 (71.03%) 123,066 (70.97%) 753 (81.76%) 1,504 (82.01%) 752 (82.01%) 752 (82.01%)
HER2 Status <0.01 >0.99
Negative 144,939 (83.15%) 144,222 (83.17%) 717 (77.85%) 1,434 (78.19%) 165 (17.99%) 165 (17.99%)
Positive 29,378 (16.85%) 29,174 (16.83%) 204 (22.15%) 400 (21.81%) 752 (82.01%) 752 (82.01%)
Breast Subtype <0.01 >0.99
HR+/HER2- 122,538 (70.30%) 121,858 (70.28%) 680 (73.83%) 1,360 (74.15%) 680 (74.15%) 680 (74.15%)
HR+/HER2+ 20,471 (11.74%) 20,308 (11.71%) 163 (17.70%) 320 (17.45%) 160 (17.45%) 160 (17.45%)
HR-/HER2+ 8,907 (5.11%) 8,866 (5.11%) 41 (4.45%) 80 (4.36%) 40 (4.36%) 40 (4.36%)
Triple negative 22,401 (12.85%) 22,364 (12.90%) 37 (4.02%) 74 (4.03%) 37 (4.03%) 37 (4.03%)
Type of
Surgery
0.13 0.68
No surgery
performed
6,631 (3.80%) 6,603 (3.81%) 28 (3.04%) 58 (3.16%) 30 (3.27%) 28 (3.05%)

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BCS 104,465 (59.93%) 103,932 (59.94%) 533 (57.87%) 1,082 (59.00%) 549 (59.87%) 533 (58.12%)
Mastectomy 63,221 (36.27%) 62,861 (36.25%) 360 (39.09%) 694 (37.84%) 338 (36.86%) 356 (38.82%)
Chemotherapy <0.01 0.58
None/
Unknown
96,035 (55.09%) 95,598 (55.13%) 437 (47.45%) 884 (48.20%) 448 (48.85%) 436 (47.55%)
Yes 78,282 (44.91%) 77,798 (44.87%) 484 (52.55%) 950 (51.80%) 469 (51.15%) 481 (52.45%)
Radiation
therapy
<0.01 0.1
None/Unknown 78,171 (44.84%) 77,813 (44.88%) 358 (38.87%) 680 (37.08%) 323 (35.22%) 357 (38.93%)
Yes 96,146 (55.16%) 95,583 (55.12%) 563 (61.13%) 1,154 (62.92%) 594 (64.78%) 560 (61.07%)
4.2. Overall Survival and Breast Cancer-Specific Survival
The median length of follow-up was 40 months for the IDC group
and 32 months for the IMPC group. Overall, patients with IMPC
had better survival outcomes than IDC patients as revealed by
both the BCSS (HR=0.57, 95% CI: 0.41-0.78, p<0.01) and OS
(HR=0.74, 95% CI: 0.58-0.94，p=0.03). However, after PSM, pa-
tients with IMPC and IDC had similar BCSS (HR=0.88, 95% CI:
0.54-1.45, p=0.62) and OS (HR=0.86, 95% CI: 0.62-1.20, p=0.45)
rates (Figure 3). In the long-term survival comparison with the
PSM group, IMPC patients had better OS rates from the 3rd to 5th
years and better BCSS rates at the 4th and 5th years after diagno-
sis(p<0.05). Further stratification analysis showed a better 5-year
BCSS (HR=0.36, 95%CI: 0.18-0.72, p<0.01) and OS (HR=0.35,
95%CI: 0.22-0.55, p<0.01) rate in the HR+/HER2- subtype (Ta-
ble 2). We conducted both univariate and multiple Cox regression
models for the PSM cohort (Table 3). In the univariate model,
IMPC was not an independent factor for either OS (p=0.36) or
BCSS (p=0.62), which was confirmed in the multivariate model
(OS p=0.24, BCSS p=0.41).
Figure 3: Kaplan-Meier survival curves of the OS and BCSS rates of the whole/PSM cohort. (a-b. OS and BCSS rate of whole cohort. b-c. OS and
BCSS rate of PSM cohort.).
Table 2: Long-term survival comparison and subtype subset analysis of IMPC and IDC in the PSM group
BCSS OS
Survival rates HR(95% CI) p Survival rates HR(95% CI) p
IMPC IDC IMPC IDC
Year of survival
1 year survival 99.5 99.9 5.02(0.59-43.07) 0.1 98.4 98.7 1.25(0.58-2.69) 0.56
2 year survival 96.9 97.1 1.04(0.61-1.78) 0.89 96.9 97.1 1.04(0.61-1.78) 0.89
3 year survival 98.3 97.1 0.59(0.31-1.09) 0.09 96.2 93.9 0.61(0.40-0.94) 0.02
4 year survival 98 96.2 0.51(0.28-0.90) 0.02 95.6 91.7 0.51(0.34-0.75) <0.01
5 year survival 97.9 95.5 0.45(0.26-0.79) <0.01 95.1 90.2 0.47(0.33-0.69) <0.01
1 year survival correlation
HR+/HER2- 99.6 99.9 3.01(0.31-29.0) 0.32 98.8 98.5 1.25(0.58-2.69) 0.64
HR+/HER2+ 100 100 1.00(1.00-1.00) >0.99 98.1 98.8 0.80(0.31-2.03) 0.65
HR-/HER2+ 97.5 100 1.03(0.98-1.08) 0.31 95,0 100 1.51(0.25-9.16) 0.15
Triple negative 97.3 100 1.03(0.97-1.08) 0.31 94.6 100 1.06(0.98-1.14) 0.15

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3 year survival correlation
HR+/HER2- 98.5 97.1 0.49(0.23-1.06) 0.07 96.9 93.4 0.45(0.27-0.76) <0.01
HR+/HER2+ 98.8 98.8 1.00(0.14-7.19) >0.99 95.6 96.9 1.42(0.44-4.57) 0.56
HR-/HER2+ 97.5 97.5 1.00(0.06-16.56) >0.99 95 97.5 2.05(0.18-23.59) 0.56
Triple negative 91.9 89.2 0.73(0.15-3.51) 0.69 86.5 86.5 1.00(0.26-3.79) >0.99
5 year survival correlation
HR+/HER2- 98.4 95.6 0.36(0.18-0.72) <0.01 96.2 89.7 0.35(0.22-0.55) <0.01
HR+/HER2+ 98.8 98.1 0.66(0.11-4.02) 0.65 94.4 95 1.13(0.43-3.01) 0.8
HR-/HER2+ 97.5 97.5 1.00(0.06-16.56) >0.99 92.5 92.5 1.00(0.19-5.28) >0.99
Triple negative 86.5 81.1 0.67(0.19-2.34) 0.53 81.1 75.7 0.73(0.24-2.21) 0.57
Table 3: Univariate and multivariate Cox proportional hazard models of overall survival (OS) and breast cancer-specific survival (BCSS) rates in the
propensity score matched analysis
Univariate Multivariate
BCSS OS BCSS OS
HR(95% CI) p HR(95% CI) p HR(95% CI) p HR(95% CI) p
Pathological type
IMPC vs.
IDC
0.88(0.52-1.47) 0.62 0.85(0.60-1.21) 0.36 0.81(0.48-1.35) 0.41 0.81(0.57-1.15) 0.24
Age
>50 vs. ≤50 1.48(0.81-2.70) 0.12 3.18(1.87-5.41) <0.01 2.51(1.32-4.79) 0.01 3.52(2.02-6.13) <0.01
Stage
I & II vs. III 6.28(3.9-10.10) <0.01 2.69(1.95-3.71) <0.01 7.37(4.17-13.01) <0.01 2.34(1.86-2.94) <0.01
Grade
I & II vs. III 2.37(1.49-3.79) <0.01 1.43(1.04-1.95) 0.03 2.09(1.26-3.44) <0.01 1.45(1.09-1.94) 0.02
Subtype
HR+/HER2- ref. 0.01 ref. <0.01 ref. <0.01 ref. <0.01
HR+/HER2+ 0.47(0.19-1.18) 0.70(0.42-1.16) 0.16 0.32(0.12-0.8) 0.02 0.70(0.41-1.18) 0.18
HR-/HER2+ 1.05(0.33-3.37) 1.22(0.60-2.50) 0.58 1.03(0.32-3.37) 0.96 1.71(0.82-3.58) 0.16
HR-/HER2- 4.72(2.52-8.86) 2.90(1.74-4.83) <0.01 3.73(1.89-7.34) <0.01 3.14(1.83-5.40) <0.01
Surgery
Mast. vs.
BCS
2.77(1.30-5.90) 0.03 3.26(1.89-5.60) <0.01 1.50(0.67-3.33) 0.32 0.59(0.32-1.11) 0.1
Chemotherapy
Yes vs. No 1.71(1.05-2.78) <0.01 0.65(0.47-0.89) 0.01 0.98(0.56-1.71) 0.93 0.48(0.33-0.70) <0.01
Radiation therapy
Yes vs. No 0.37(0.23-0.59) <0.01 0.34(0.25-0.47) <0.01 0.33(0.2-0.57) <0.01 0.32(0.22-0.46) <0.01
*Mast.= mastectomy
4.3. HR+/HER2- Invasive Micropapillary Carcinoma Had
Better Long-Term Survival Outcomes
91.5% of the IMPC and 82% of the IDC were luminal type (HR+,
Her2-/+) (p<0.01, Mann-Whitney U-test) respectively. Therefore,
it is necessary to confirm weather higher propotions of luminal
subtype influence IMPC prognosis. In the PSM cohort, we per-
formed a subgroup analysis based on breast subtype. The OS rate
of IMPC was significantly better than that of IDC for the HR+/
HER2- type (HR=0.65, 95% CI: 0.44-0.98, p=0.04) but the BCSS
rate was similar (HR=1.31, 95% CI: 0.68-2.52, p=0.19). (Figure
4) In the HR+/HER2- subtype, IMPC and IDC patients received
similar treatments, including surgery (p=0.27), chemotherapy
(p=0.99), and radiotherapy (p=0.28) (Mann-Whitney U-test). Uni-
variate and multivariate Cox regression models were performed in
the HR+/HER2- subset, and IMPC was an independent prognostic
factor for OS (Table 4).
Table 4: Univariate and multivariate Cox proportional hazard models of overall survival (OS) and breast cancer-specific survival (BCSS) rates in the
HR+/HER2- subset in the propensity score matched analysis.
Univariate Multivariate
BCSS OS BCSS OS
HR(95% CI) p HR(95% CI) p HR(95% CI) p HR(95% CI) p
Pathological type
IMPC vs.
IDC
0.68(0.35-1.29) 0.24 0.63(0.41-0.97) 0.04 0.59(0.31-1.12) 0.1 0.58(0.38-0.90) 0.01
Age
>50 vs. ≤50 1.15(0.58-2.30) 0.69 2.72(1.46-5.05) <0.01 1.90(0.90-4.01) 0.09 2.83(1.47-5.43) <0.01
Stage
I & II vs. III 6.43(3.68-11.21) <0.01 2.53(1.72-3.71) <0.01 5.42(2.82-10.45) <0.01 3.47(2.20-5.48) <0.01
Grade
I & II vs. III 2.86(1.65-4.96) <0.01 1.60(1.10-2.32) 0.01 2.54(1.43-4.49) <0.01 1.74(1.19-2.55) 0.01
Surgery
Mast vs. BCS 4.59(2.08-10.11) <0.01 3.99(2.17-7.36) <0.01 2.91(1.26-6.74) 0.01 2.32(1.24-4.37) 0.01
Chemotherapy
Yes vs. No 2.00(1.14-3.50) 0.02 0.73(0.50-1.06) 0.1 1.24(0.64-2.40) 0.53 0.62(0.40-0.97) 0.04
Radiation therapy
Yes vs. No 0.34(0.20-0.59) <0.01 0.33(0.23-0.47) <0.01 0.34(0.18-0.64) <0.01 0.32(0.21-0.49) <0.01

6. clinicsofoncology.com 6
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Figure 4: Kaplan-Meier survival curves of the OS and BCSS rates of HR+/HER2- in the PSM cohort.
5. Discussion
Our data were collected from the latest SEER database (Novem-
ber 2019 submission). In this large, population-based cohort, we
included more patients than a previous study and incorporated re-
cords of HER2 status entered after 2010. Over 49% of patients
with IMPC had axillary lymph node involvement, while only
31% of IDC patients had regional metastasis. We observed that
IMPC had a better survival than IDC in OS and BCSS in whole
cohort, but not significant in PSM cohort, even IMPC had more
axillary lymph node metastasis. Furthermore, IMPC metastasized
more than IDC at any T stage (p<0.05). In the whole cohort, IMPC
was associated with a better outcome than IDC, but similar af-
ter PSM; however, IMPC patients had better survival outcomes
at 4 and 5 years after diagnosis (p<0.05). Additional univariate
and multivariate Cox regression models revealed that IMPC was
not an independent factor for prognosis (p>0.05). Stratification
analysis indicated a better OS outcome of HR+/HER2- subtype
IMPC (HR=0.65, p=0.04). In addition, a comparison of the distant
metastasis rate was performed, and we found IMPC had less M1
patients than IDC after PSM (p=0.01) but similar in whole cohort
(p=0.22). In stratified analysis, only HR+/HER2- subtype IMPC
metastasized less than IDC in distant location (Supplement Table
1). IMPC patients exhibited more lymph node metastasis than IDC
patients but similar survival outcomes to IDC patients, which was
similar to the previous studies [7,8,11]. However, IMPC patients
had a better survival tendency, especially at 4 and 5 years after di-
agnosis. The prognosis of IMPC remains controversial. Chen and
Fan et al. (2008) reported that IMPC is a more aggressive tumor
with a poorer prognosis [14]. Ga Young Yoon et al. (2019) dis-
covered worse recurrence-free survival (RFS) rates for IMPC than
IDC [15]. However, Chen and Paulino et al. (2014) discovered that
IMPC had better DSS and OS rates than IDC [16]. Chen and Wu et
al. (2017) found that IMPC and IDC patients had comparable OS
and BCSS rates before and after propensity score matching [17].
In addition, Hao et al. (2018) found no differences in OS and DFS
rates between IMPC and IDC patients [18]. Some of the above
studies applied propensity score matching to the whole cohort;
however, few achieved a good balance of the basic characteristics,
which might have affected the outcome of the comparison. Our
study included 173,396 IDC and 921 IMPC patients and achieved
perfect matches for age, AJCC stage, grade, and HR HER2 status
after PSM. Although no differences were observed in treatment
(p>0.05), IMPC patients tended to have better outcomes. We per-
sumed that advanced therapy might be applied causing a better
outcome. In the PSM cohort, IMPC patients received higher rates
of radiation therapy and mastectomy surgery, which could influ-
ence the long-term survival rate. Unlike the findings reported in
other studies, we unexpectedly observed that HR+/HER2- IMPC
patients had a better long-term survival rates than IDC patients.
A previous study indicated that the prevalence of the HR+ type is
high in IMPC [19] and that the TNBC subtype is associated with
worse prognosis[20]. In our research, 91.5% of IMPC patients
were HR+/HER2- type which had the best prognosis among all
breast cancer subtypes. Combined with the finding that the HR+/
HER2- type was associated with favorable OS rates in the PSM
cohort, we could assume that IMPC had a better prognosis due to
a higher proportion of the HR+/HER2- subtype. The IMPC distant
metastasis rate was similar to that of IDC in whole cohort, but less
in PSM cohort. Deman F et al. found a low rate of distant recur-
rences of stage I-III IMPCs treated with primary surgery, despite
a high proportion of grade 3 tumors and lymph node involvement
[21], but the study only included 105 IMPC patients. Tang et al.
found that IMPC had a higher rate of distant metastasis [22], but
this study included more triple-negative subtypes of IMPC (IMP-
C:IDC 21.8% vs 1.4%, p<0.01), while TNBC metastasized more
than other subtypes. Kaya C et al. discovered that between two
groups divided by IMPC component ratio (≤75% and >75%), no
differences in distant metastasis were found [23]. We propose that
despite its aggressive lymph invasion ability, IMPC lacked traits
for distant metastasis, and the mechanism within still needs to be
studied. There were some flaws within our study. We collected data
from over 921 IMPC patients from the SEER database, but a series
of clinical characteristics were absent, such as chemotherapy reg-
imens, hormone therapy, target treatment, menopausal status, etc.
Therefore, selection bias is inevitable.

7. clinicsofoncology.com 7
Volume 6 Issue 6 -2022 Research Article
Supplement Table 1: Comparison of distant metastasis rate
Whole cohort PSM cohort
All M0 M1 p All M0 M1 p
Overall 0.22 0.01
IDC 180,955 173,643(95.96%) 7,312(4.041 953 900(94.44%) 53(5.56%)
IMPC 953 922(96.75%) 31(3.25%) 953 922(96.75%) 31(3.25%)
HR+/HER2- 0.53 0.04
IDC 125,952
122,000
(70.26%)
3,952 (54.05%) 699 665 (73.89%) 34 (64.15%)
IMPC 699 680 (73.75%) 19 (61.29%) 699 680 (73.75%) 19 (61.29%)
HR+/HER2+ 0.22 0.05
IDC 21,746 20,349 (11.72%) 1,397 (19.11%) 171 155 (17.22%) 16 (30.19%)
IMPC 171 164 (17.79%) 7 (22.58%) 171 164 (17.79%) 7 (22.58%)
HR-/HER2+ 0.41 >0.99
IDC 9,666 8,886 (5.12%) 780 (10.67%) 43 41 (4.56%) 2 (3.77%)
IMPC 43 41 (4.45%) 2 (6.45%) 43 41 (4.45%) 2 (6.45%)
HR-/HER2- 0.47 0.31
IDC 23,591 22,408 (12.90%) 1,183 (16.18%) 40 39 (4.33%) 1 (1.89%)
IMPC 40 37 (4.01%) 3 (9.68%) 40 37 (4.01%) 3 (9.68%)
6. Conclusion
In summary, IMPC metastasized to more axillary lymph nodes
than IDC but the distant metastasis rate was similar. Despite ag-
gressive regional invasion, IMPC had a similar overall survival
and breast cancer specific survival outcome to IDC. However,
HR+/HER2- IMPC had a better overall survival rate than IDC.
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